Many types of processes are known for the manufacture of sandwich molded articles. Generally, said processes enable one to produce only articles having a very simple shape, such as parisons for blow-molded bottles, as disclosed in EP-A-0325440. According to this document, in order to obtain a sandwich parison having an inner layer of PET, an intermediate layer of EV-OH and an external layer of PET, a coaxial injection nozzle is used, and the PET resin is injected before and after injection of the EV-OH resin. A stopping time between first and second injections is provided, while second and third injections are carried out in part simultaneously. The resins, paths are thermally insulated in order to maintain the required different temperatures as far as possible.
U.S. Pat. No. 5,167,896 (Hirota) discloses the coinjection of a resin surface material and a core of fiber-reinforced resin mixture to manufacture a cabinet for use with a display.
Only a portion of the obtained cabinet has a sandwich structure with inner core and two external layers. In fact, coinjection is not an easy process and it becomes even more difficult to control where the required molded article has a geometrically complex shape.
EP-A-93108241.6 discloses an apparatus for coinjection molding provided with several nozzles for one cavity of the mold.